Molecular phylogeny and dating reveals an Oligomiocene radiation of dry-adapted shrubs (former Tremandraceae) from rainforest tree progenitors (Elaeocarpaceae) in Australia

Abstract

To better understand the historical biogeography of the southern hemisphere and evolutionary responses of plants to aridity, we undertook a detailed phylogenetic study of the predominantly southern family Elaeocarpaceae sensu lato (including Tremandraceae). Plastid trnL-trnF and nuclear ITS sequence data were analyzed using parsimony and Bayesian methods and molecular evolutionary rates calibrated using the Oligocene fossil record of Elaeocarpus mesocarps to estimate the minimum divergence dates. The results indicate the monophyly of all recognized genera and a placement for the former Tremandraceae (three genera and about 49 species of shrubby, dry-adapted Australian plants) within the widespread predominantly rainforest tree family Elaeocarpaceae (nine genera, over 500 species). The former Tremandraceae clade diverged from its sister (Aceratium + Elaeocarpus+Sericolea) during the Paleocene, after which it underwent a marked acceleration in evolutionary rate. Furthermore, this lineage diversified during the late Miocene, coincident with widespread aridification in Australian environments and extensive radiations of several sclerophyllous groups. The role of dispersal in explaining the current geographical distribution of Elaeocarpaceae is illustrated by Aristotelia. This genus, whose distribution was previously thought to reflect Gondwanan vicariance, is shown to have arrived in New Zealand from Australia at least 6-7 million yr ago.